This project is concerned with our continued investigation of biological techniques for immunosuppression. Our primary interest is that of passive enhancement. In rodents, serum and antigen are used to produce enhancement of rat allografts and in dogs and humans, F(ab')2 fragments of immunoglobulin are required. As an important part of this investigation, in vitro identification of various types of immune responses, using 15Cr-release assays, will be studied in a variety of settings. In rodents, infiltrating cells in allografts will be characterized and their function identified. Also, allogeneic and xenogeneic models for observing responses to administered tumor cell antigens will be used. A new type of immune response, apparently associated with antigen-antibody complex formation will be studied in great depth. Investigations will be performed in dogs with passive enhancement using F(ab')2 fragments from anti "B cell" serum, to determine if this provides more efficient enhancement. Finally, a clinical prospective, randomized protocol for passive enhancement of renal transplant recipients using multispecific F(ab')2 fragments will be activated. BIBLIOGRAPHIC REFERENCES: Wilson, R.E., Sonis, S.T., and Stelos, P.: Monitoring of immune responses to tumor antigens: The role of antigen-antibody complexes and excess antigen or antibody. Europ. Surg. Res. 8:68, 1976. Busch, G. J., Martins, A. C. P., Hollenberg, N.K., Moretz, R. C., Wilson, R. E. and Coleman, R. W.: Successful short-term modification of hyperacute renal allograft rejection in the primate: intrarenal effects of phenoxybenzamine and methyl-prednisolone combined with heparin. Amer. J. Path. 82: 43, 1976.